The quake did not cause fresh damage to the crippled Fukushima Daiichi nuclear plant, according to its operator Tokyo Electric Power.

There were no immediate reports of damage or injuries, while the Pacific Tsunami Warning Center said there was "no destructive widespread tsunami threat" although a local tsunami could result from a quake of this size.

The Tohoku Shinkansen bullet train services were halted because of the quake, but resumed shortly afterwards.

The devastating March 11 twin disasters left about 22,000 people dead or missing and triggered an atomic crisis at the Fukushima plant, where emergency workers are still working to cool down the overheating reactors.